Related Articles

Waiting for roses (Rosa spp.) to blossom each spring is an enjoyable test of patience. Swirling through a glorious change from the first traces of color brightening their hard, green surfaces to their fully open flowers, rosebuds undergo this transformation across U.S. Department of Agriculture plant hardiness zones 2 through 10. All too often, however, disease intervenes to blemish rosebuds or -- in the worst cases -- stop their bloom.

Powdery Mildew

Even though your rosebuds are baby roses, finding them coated with what looks like layers of baby powder is cause for alarm. What you're actually seeing is a powdery-mildew outbreak following infestation of the Sphaerotheca pannosa fungus. Although powdery mildew usually attacks a rose's foliage, it's capable of infecting shoots and buds as well. In its advanced stages, the disease distorts and curls foliage and stunts a rose's growth. Powdery mildew targets closely spaced, shaded roses during dry, warm weather with temperatures in the low 70-degree Fahrenheit range.

Powdery Mildew Control

Planting your roses in full sun with adequate air circulation, allowing 3 feet between hybrid teas and 4 or more feet between larger varieties, discourages powdery mildew. Wetting the plants when you water rinses off spores already on them. Clearing and destroying infected debris from the rose bed and pruning infected plant parts eliminate them as spore sources. If these measures aren't sufficient, spray your roses with a preventive solution of 4 tablespoons of dusting wettable sulfur in 1 gallon of water -- or at the label's recommended concentration -- as soon as their new growth emerges in spring. Use wettable sulfur at temperatures below 90 degrees F. Repeat the application weekly while conditions favor the disease, or after rainfall.

Gray Mold

Damp days with temperatures between 70 and 77 degrees F invite airborne gray mold (Botrytis cinerea) spores to attack wet, damaged rose flowers and buds. Injuries as minor as rainwater bruising are enough to give gray mold an opportunity. Infected rosebuds develop layers of furry, grayish to brown mold. Many of them remain closed, and those that open have brown, withered petals. In Mediterranean climates, gray mold is most active in fall and early spring, or during foggy, damp coastal summers. Elsewhere, it's most threatening during rainy springs.

Gray Mold Control

If you purchase bare-root roses by mail order, remove them from their shipping sleeves as quickly as possible. Gray mold spores flourish in the moist, cool environment within the sleeves. Other preventive measures include spacing the plants properly, promptly removing damaged or dying flowers and buds as well as fallen debris and keeping the foliage dry when you water. Treat infected roses by pruning and disposing of their diseased canes, buds and flowers.

Disease-Mimicking Insects

Sap- and pollen-consuming thrips (Thrips spp.) less than 1/20 inch long tunnel into rose buds without difficulty. Infested buds are deformed, with brown-edged petals. They remain partially or completely closed. The pests typically attack a rose's first set of buds in late spring or early summer. Petal-peppering black waste distinguishes thrips damage from the early symptoms of gray mold. Spraying emerging buds on alternate days with a solution of 5 tablespoons of detergent-free liquid soap in 1 gallon of water may destroy the pests before they do serious damage.

About the Author

Passionate for travel and the well-written word, Judy Wolfe is a professional writer with a Bachelor of Arts in English literature from Cal Poly Pomona and a certificate in advanced floral design. Her thousands of published articles cover topics from travel and gardening to pet care and technology.